Available data on the mechanism of Mg absorption is mainly descriptive in nature. There is data to support the existence of both gradient-driven and saturable Mg absorption. It is not clear, however, which process predominates under normal conditions. Evidence for a saturable process is based on a curvilinear relationship between dietary or luminal [Mg] and Mg uptake. Whether this is due to a carrier-mediated mechanism or due to alterations in absorption through the paracellular route remains to be determined. A careful review of the literature indicates that the predominate site of Mg absorption is the distal small intestine. Most of these studies, however, have been done in isolated segments which may not adequately reflect absorption in an undisturbed gastrointestinal tract. Future work will need to focus on identifying and characterizing Mg transport at the cellular and paracellular level as well as developing more sophisticated strategies for examining Mg absorption in the whole animal.